Method for reducing thin films on low temperature substrates

ABSTRACT

A method for producing an electrically conductive thin film on a substrate is disclosed. Initially, a reducible metal compound and a reducing agent are dispersed in a liquid. The dispersion is then deposited on a substrate as a thin film. The thin film along with the substrate is subsequently exposed to a pulsed electromagnetic emission to chemically react with the reducible metal compound and the reducing agent such that the thin film becomes electrically conductive.

RELATED APPLICATION

The present application is a continuation-in-part of U.S. Ser. No.11/720,171, filed on May 24, 2007, entitled “Electrical, Plating andCatalytic Uses of Metal Nanomaterial Composition,” which is incorporatedherein by reference.

The present application is related to U.S. Ser. No. 61/196,531, filed onOct. 17, 2008, entitled “Method and Apparatus for Reacting Thin Films onLow Temperature Substrates at High Speeds,” which is incorporated hereinby reference.

BACKGROUND OF THE INVENTION

1. Technical Field

The present invention relates to curing method in general, and, inparticular, to a method for reducing thin films on low-temperaturesubstrates.

2. Description of Related Art

One approach to making electronic circuits is to print electricalconductors with metallic ink onto a substrate, and the substrate is thenheated to sinter the particles of the metallic ink in order to formelectrical conducting traces. Generally, most printed metals suitablefor electrically conduction need to be heated to a very hightemperature, often within a couple hundred degrees centigrade of theirmelting point, in order to sinter and become conductive.

Two of the most pursued elements for making conductive traces in printedelectronics are silver and copper. Silver has two advantages over copperbecause silver can be heated in air with minimal oxidation and that itsoxides, which are comparatively low in conductivity, decompose atrelatively low temperatures. These two qualities, coupled with the factthat silver is the most electrically conductive metal often outweigh itshigh cost when making conductive traces. Thus, even though copper hasabout 90% of the conductivity of silver and it is usually 50-100 timescheaper on a mass basis, silver inks still dominate the printedelectronics market because the additional cost of making and processingcopper inks to avoid oxidation is generally higher than the differencein material costs.

It is well-known in the prior art that some metal oxides can be reducedby hydrogen or hydrocarbons at an elevated temperature if they have apositive reduction potential. For example, copper can be first extractedby mixing copper oxide bearing ore with charcoal along with anapplication of heat. When oxidized copper particles or even pure copperoxide is heated in the presence of a reducer, the oxidized copperparticles can sinter to form a conductor.

When making thin film conductors by printing copper particles, a veryconductive trace can be formed if the particles are heated to theirsintering temperature in an inert or reducing atmosphere. Since themelting point of copper is nearly 1,085° C., the temperature requiredfor sintering dictates that only high temperature substrates such asglass or ceramic can be used. Such high-temperature requirement preventsthe usage of inexpensive substrates such as paper or plastic.

Alternatively, if a copper particle film is deposited on alow-temperature substrate, it can be heated to near the substrate'sdecomposition temperature and then be placed in a reducing atmosphere,but the low temperature dramatically increases the amount of time neededfor curing from seconds to minutes or even hours, depending on thethickness of the film and the temperature. At low temperatures,sintering is very limited, and thus the film resistivity becomes high.Furthermore, the need for an inert or reducing atmosphere alsodramatically increases processing cost. Thus, it would be desirable toprovide an improved method for rapidly reducing metal oxide onlow-temperature substrates in ambient atmosphere.

SUMMARY OF THE INVENTION

In accordance with a preferred embodiment of the present invention, areducible metal compound and a reducing agent are initially dispersed ina liquid, such as water. The dispersion is then deposited on a substrateas a thin film. The thin film along with the substrate is subsequentlyexposed to a pulsed electromagnetic emission to chemically react withthe reducible metal compound and the reducing agent such that the thinfilm becomes electrically conductive.

All features and advantages of the present invention will becomeapparent in the following detailed written description.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention itself, as well as a preferred mode of use, furtherobjects, and advantages thereof, will best be understood by reference tothe following detailed description of an illustrative embodiment whenread in conjunction with the accompanying drawings, wherein:

FIG. 1 is a flow diagram of a method for curing a thin film on alow-temperature substrate, in accordance with a preferred embodiment ofthe present invention; and

FIG. 2 is a diagram of a curing apparatus, in accordance with apreferred embodiment of the present invention.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT

For the present invention, curing is defined as thermal processing,which includes reducing a metal compound contained within a thin film ona low-temperature substrate. A thin film is defined as a coating of lessthan 100 microns thick. Examples of low-temperature substrates includepaper, plastic or polymer.

The present invention is a method for providing activation energy toperform a reduction-oxidation reaction in a thin film using intensepulsed light. The redox reaction may be the reduction of a metal oxideby an organic compound and may be performed on a low-temperaturesubstrate.

Referring now to the drawings and in particular to FIG. 1, there isdepicted a flow diagram of a method for curing a thin film on alow-temperature substrate, in accordance with a preferred embodiment ofthe present invention. Starting in block 100, a non-conducting metaloxide is dispersed in a liquid, such as water, using any number ofcommon dispersing agents such as polyvinylpyrrolidone orpolystyrene-acrylate copolymers, as shown in block 110. The dispersionalso includes at least one reducing agent. The reducing agent may be anyof a number of compounds including alcohols, aldehydes, carboxylic acidsand carbon black. Reducing agents preferably include glycerol, ascorbicacid, 1,2-hexanediol and glutaric acid. Other additives may includevarious surfactants for surface wetting, humectants, co-solvents, andbinder resins. The dispersion may include conducting particles such assilver, copper, or gold. The dispersion may also contain partiallyoxidized metal particles. The non-conducting metal oxide can be anymetal oxide listed in Table I.

TABLE I MoO₂, MoO₃ molybdenum oxide WO₂, WO₃ tungsten oxide ReO₂, Re₂O₅,ReO₃ rhenium oxide FeO, Fe₂O₃ iron oxide RuO₂ ruthenium oxide OsO₂osmium oxide CoO, Co₃O₄ cobalt oxide Rh₂O₃, RhO₂ rhodium oxide IrO₂iridium oxide NiO nickel oxide PdO palladium oxide PtO₂ platinum oxideCu₂O, CuO copper oxide Ag₂O silver oxide Ag₂O₃ gold oxide ZnO zinc oxideCdO cadmium oxide In₂O₃ indium oxide GeO, GeO₂ germanium oxide SnO, SnO₂tin oxide PbO, PbO₂ lead oxide Sb₂O₃, Sb₂O₄, Sb₂O₅ antimony oxide Bi₂O₃bismuth oxide

The dispersion is then deposited on a low-temperature substrate as athin film, as depicted in block 120. The low-temperature substrate canbe polymer (polyimide, polyethylene terephthalate, polyethylenenaphthalate, polyethylene, polycarbonate, polystyrene, polyvinylchloride, etc.), paper, etc. The dispersion may be deposited on alow-temperature substrate by any common printing technique includinginkjet, gravure, flexographic, rollcoating, screen-printing and thelike. Conversely, the non-conducting metal oxide and reducer (i.e.,reducing agent) may be deposited on a low-temperature substrate as athin film using a dry deposition process such as xerography.

The thin film along with the low-temperature substrate are subsequentlyexposed to a pulsed electromagnetic emission in order to initiate aredox reaction between the non-conducting metal oxide and reducer on thelow-temperature substrate, as shown in block 130. The pulsedelectromagnetic source can be a laser, flash lamp, directed plasma arclamp, microwave, or radiofrequency induction heater capable ofdelivering a pulse length of less than 20 ms. An alternative embodimentis the use of an electron beam or intense arc lamp to deposit heat intothe film to initiate the redox reaction as the film is being conveyedpast the source of radiation. For the electron beam and arc lampsources, the combination of a moving substrate and a static source hasthe effect of providing pulsed heating of the film. The electromagneticsource should have an emission greater than 500 W/cm². As a result ofthe exposure, the thin film is rendered electrically conductive afterthe redox reaction.

Preferably, the thin film is cured while the low-temperature substrateis being conveyed past the light source using an automated curingapparatus as described below.

With reference now to FIG. 2, there is illustrated a diagram of a curingapparatus for curing thin films on low-temperature substrates, inaccordance with a preferred embodiment of the present invention. Asshown, a curing apparatus 200 includes a conveyor system 210, a strobehead 220, a relay rack 230 and a reel-to-reel feeding system 240. Curingapparatus 200 is capable of curing a thin film 202 mounted on alow-temperature substrate 203 situated on a web being conveying paststrobe head 220 at a relatively high speed. Conveyor system 210 canpreferably operate at speeds from 2 to 1000 feet/min to move substrate203. Curing apparatus 200 can preferably accommodate a web width of anywidth in 6-inch increments. Thin film 202 can be added on substrate 203by one or combinations of existing technologies such as screen-printing,inkjet printing, gravure, laser printing, xerography, pad printing,painting, dip-pen, syringe, airbrush, flexographic, CVD, PECVD,evaporation, sputtering, etc. The deposition of thin film 202 ontosubstrate 203 may be performed inline with the curing process.

Strobe head 220, which is preferably water cooled, includes ahigh-intensity pulsed xenon flash lamp 221 for curing thin film 202located on substrate 203. Pulsed xenon flash lamp 221 can provide pulsesof different intensity, pulse length, and pulse repetition frequency.For example, pulsed xenon lamp 221 can provide 10 μs to 10 ms pulseswith a 3″ by 6″ wide footprint at a pulse repetition rate of up to 1kHz. The spectral content of the emissions from pulsed xenon flash lamp221 ranges from 200 nm to 2,500 nm. The spectrum can be adjusted byreplacing the quartz lamp with a cerium doped quartz lamp to remove mostof the emission below 350 nm. The quartz lamp can also be replaced witha sapphire lamp to extend the emission from approximately 140 nm toapproximately 4,500 nm. Filters may also be added to remove otherportions of the spectrum. Flash lamp 221 can also be a water wall flashlamp that is sometimes referred to as a Directed Plasma Arc (DPA) lamp.

Relay rack 230 includes an adjustable power supply, a conveyance controlmodule, and a strobe control module. The adjustable power supply canproduce pulses with an energy of up to 4 kilojoules per pulse.Adjustable power supply is connected to pulsed xenon flash lamp 221, andthe intensity of the emission from pulsed xenon flash lamp 221 can bevaried by controlling the amount of current passing through pulsed xenonflash lamp 221.

The adjustable power supply controls the emission intensity of pulsedxenon flash lamp 221. The power, pulse duration and pulse repetitionfrequency of the emission from pulsed xenon flash lamp 221 areelectronically adjusted and synchronized to the web speed to allowoptimum curing of thin film 202 without damaging substrate 203,depending on the optical, thermal and geometric properties of thin film202 and substrate 203.

During the curing operation, substrate 203 as well as thin film 202 arebeing moved by conveyor system 210. Conveyor system 210 moves thin film202 under strobe head 220 where thin film 202 is cured by rapid pulsesfrom pulsed xenon flash lamp 221. The power, duration and repetitionrate of the emissions from pulsed xenon flash lamp 221 are controlled bystrobe control module, and the speed at which substrate 203 is beingmoved past strobe head 220 is determined by conveyor control module.

A sensor 250, which can be mechanical, electrical, or optical, isutilized to sense the speed of conveyor system 210. For example, theconveyor belt speed of conveyor belt system 210 can be sensed bydetecting a signal from a shaft encoder connected to a wheel that makescontact with the moving conveyor belt. In turn, the pulse repetitionrate can be synchronized with the conveyor belt speed of conveyor beltsystem 210. The synchronization of the strobe pulse rate f is given by:f=0.2*s*o/wwhere

-   -   s=web speed [ft/min]    -   o=overlap factor    -   w=curing head width [in]        Overlap factor is the average number of strobe pulses that are        received by a substrate at any one location. For example, with a        web speed of 200 ft/min, an overlap factor of 5, and a curing        head width of 2.75 inches, the pulse rate of the strobe is 72.7        Hz.

When flash lamp 221 is pulsed, thin film 202 is momentarily heated toprovide activation energy for a redox reaction. When a rapid pulse trainis combined with moving substrate 203, a uniform cure can be attainedover an arbitrarily large area as each section of thin film 202 may beexposed to multiple pulses, which approximates a continuous curingsystem such as an oven.

Unlike the prior art, in which reducers or fluxes have been introducedto remove oxide from metal particles before curing, the method of thepresent invention places a reducer directly in a thin film along withthe oxide to be reduced by an intense pulsed light. The process can beperformed in air because the requirement of an inert or reducingenvironment is obviated by the brief time of the reaction. Basically,the thin film is heated briefly to a high enough temperature in orderfor the reducer and the oxide to react, but the time of the reaction isbrief enough to prevent significant chemical reaction with the air.

As a result of the intense pulsed light, the metal oxide is reduced bythe reducer in the film resulting in a thin film of metal. Although theradiated power per unit area from the pulsed light source is very high(˜2 KW/cm²), the pulse duration is so short that little energy (˜2J/cm²) is deposited on substrate 103. Hence, substrate 103 is undamaged.Thus, the method of present invention allows a high-temperature redoxreaction to occur on a thermally fragile substrate such a plastic orpaper. The process happens so quickly that oxidation of the metal in airis minimal, so an inert or reducing atmosphere is not needed. Inaddition to reducing the metal oxide, the intense pulsed light has theadded benefit of sintering the metal particles to form a highlyconductive trace without damaging the substrate. Both the reduction andthe sintering appear to happen from each pulse of light.

As an alternative embodiment, the reducer is a metal with a negativereduction potential, such as aluminum, magnesium, or lithium. Thisallows the reduction of materials that do not have a positive reductionpotential. The reducing metal may be in particulate or film form.

As another alternative embodiment, a method for cleaning or reactingwith a surface is performed by depositing a reacting film on a surfaceand exposing the film to an intense pulsed light to react the film withthe surface. In short, a relatively innocuous chemical heated to a veryhigh temperature can have a similar chemical activity as a relativelydangerous one at room temperature. Applications include cleaning agents,surface preparation, etc. Since a relatively innocuous agent is onlyvery active at high temperature, this means that a safer, andpotentially more environmental cleaning agent can be used in place of amore dangerous one. Storage of such an agent is safer, and disposal ofthe agent after use is more inexpensive and environmental.

The following paragraph illustrates what is happening to a thin filmduring the process of the present invention. A typical thickness of athin film is 1 micron, and the typical thickness of a substrate is 150microns (6 mils). A preferred pulse on a copper oxide/organic reducerbased films is 330 V with a 1,000 microsecond pulse length. This settingcorresponds to a radiant exposure of 1.7 J/cm² or an average radiatedpower of 1.7 KW/cm². Ignoring the radiation losses, energy absorbed byevaporation of solvent, energy absorbed by melting of the PET at theinterface of the thin film, and energy liberated from the redox reactionbeing performed a thermal simulation of the system assuming naturalconvection losses at the interfaces. Assuming the curing apparatus fromFIG. 1 is at room temperature (25° C.) before the pulse, the calculatedthe peak temperature of the thin film at the end of the 1 ms pulse isabout 1,040° C. The entire film/substrate returned to below thepublished 150° C. decomposition temperature of PET within 25 ms. Thisheating is performed with no apparent damage to the substrate. However,unlike a typical convection oven set at the published decompositiontemperature of PET, the considerably higher peak temperature providesample activation energy for the redox reaction to occur. Since the redoxreaction is certainly completed in a time frame shorter than 25 ms,there is not adequate time for the copper to be oxidized by the air.Hence, the redox reaction occurs and oxidation of the copper does not.Thus, a highly conductive copper film is created. Also, given thetemperature that the thin film reaches, the resulting copper particlesare also sintered by the pulse of light. The sintering has the effect ofincreasing both the electrical conductivity and stability of the film.

One advantage of the method of the present invention is that thereduction can be completed very rapidly, which makes it compatible withhigh-speed printing and web handling techniques. As a result, hightemperature processing can be performed on inexpensive, low temperaturesubstrates such as paper, plastic, or polymer. Another advantage of themethod of the present invention is that the reduction can be performedin an ambient environment such as air. A further advantage of the methodof the present invention is that copper, oxidized copper, or even copperoxide can be deposited on substrates and cured to resistivities rivalingprinted silver at a cost dramatically lower than silver. Morespecifically, copper oxidizes when it is heated in air. This inventionallows the curing of copper particles in air rendering a highlyconductive film regardless of their level of oxidation.

As has been described, the present invention provides a method forrapidly reducing thin films on low-temperature substrates.

EXAMPLES Example 1 Ascorbic Acid Reducer

A copper oxide dispersion was produced by mixing 3.0 g<50 nm copper (II)oxide, 3.6 g deionized water, 0.15 g PVP K-30, 0.3 g ethylene glycol,0.04 g Tergitol® TMN-6, 0.02 g Dynol® 604, 0.02 g BYK®-020, and 0.66 gascorbic acid in a 20 mL vial. 5 g of zirconium oxide milling media wasadded and the vial was agitated for 60 minutes.

The dispersion was applied to a sheet of Melinex® ST505 PET by drawdownusing a #5 Meyer bar.

The sample was cured with a pulse length of 1,000 microseconds, andoverlap factor of 2 at 24 feet per minute in an air environment.Although the film was not electrically conductive, the color of the filmchanged from dark brown to a copper color indicating significantconversion of the copper oxide to copper.

Example 2 Ethylene Glycol/Glycerol Reducer

A copper oxide dispersion was produced by mixing 2.0 g NanoArc® copperoxide, 5.7 g deionized water, 0.10 g PVP K-30, 0.6 g ethylene glycol,0.03 g Tergitol® TMN-6, 0.01 g Dynol® 604, and 0.32 g glycerol in a 20mL vial. 5 g of zirconium oxide milling media was added and the vial wasagitated for 60 minutes.

The dispersion was applied to a sheet of Melinex® ST505 PET by drawdownusing a #5 Meyer bar.

The sample was cured with a pulse length of 850 microseconds, andoverlap factor of 2 at 24 feet per minute in an air environment.Although the film was not electrically conductive, the color of the filmchanged from dark brown to a copper color indicating significantconversion of the copper oxide to copper.

Example 3 Ethylene Glycol/Glycerol Reducer

A copper oxide dispersion was produced by mixing 2.0 g NanoArc® copperoxide, 5.4 g deionized water, 0.10 g PVP K-30, 0.6 g ethylene glycol,0.03 g Tergitol® TMN-6, 0.01 g Dynol® 604, and 0.67 g glycerol in a 20mL vial. 5 g of zirconium oxide milling media was added and the vial wasagitated for 60 minutes.

The dispersion was applied to a sheet of Melinex® ST505 PET by drawdownusing a #5 Meyer bar.

The sample was cured with a pulse length of 1,000 microseconds, andoverlap factor of 3 at 24 feet per minute in an air environment.Although the film was not electrically conductive, the color of the filmchanged from dark brown to a copper color indicating significantconversion of the copper oxide to copper.

Example 4 Ethylene Glycol/Glycerol Reducer

A copper oxide dispersion was produced by mixing 2.0 g NanoArc® copperoxide, 4.9 g deionized water, 0.10 g PVP K-30, 0.5 g ethylene glycol,0.03 g Tergitol® TMN-6, 0.01 g Dynol® 604, and 1.32 g glycerol in a 20mL vial. 5 g of zirconium oxide milling media was added and the vial wasagitated for 60 minutes.

The dispersion was applied to a sheet of Melinex® ST505 PET by drawdownusing a #5 Meyer bar.

The sample was cured with a single pulse at 750V with a pulse length of2,300 in an air environment. The color of the film changed from darkbrown to a copper color indicating significant conversion of the copperoxide to copper. The sheet resistance of the film was 4.1 Ω/sq.

Example 5 Glucose Reducer

A copper oxide dispersion was produced by mixing 1.75 g NanoArc® copperoxide, 5.3 g deionized water, 0.09 g PVP K-30, 0.6 g ethylene glycol,0.02 g Tergitol® TMN-6, 0.01 g Dynol® 604, and 0.79 g glucose in a 20 mLvial. 5 g of zirconium oxide milling media was added and the vial wasagitated for 60 minutes.

The dispersion was applied to a sheet of Melinex® ST505 PET by drawdownusing a #5 Meyer bar. Separately, the dispersion was applied to a sheetof Epson Photo Paper by drawdown using a #5 Meyer bar.

The sample was cured with a pulse length of 400 microseconds, andoverlap factor of 2 at 24 feet per minute for three passes in an airenvironment. Although the film was not electrically conductive, thecolor of the film changed from dark brown to a copper color indicatingsignificant conversion of the copper oxide to copper.

Example 6 Glucose Reducer

A copper oxide dispersion was produced by mixing 1.75 g NanoArc® copperoxide, 5.3 g deionized water, 0.09 g PVP K-30, 0.6 g ethylene glycol,0.02 g Tergitol® TMN-6, 0.01 g Dynol® 604, and 1.59 g glucose in a 20 mLvial. 5 g of zirconium oxide milling media was added and the vial wasagitated for 60 minutes.

The dispersion was applied to a sheet of Melinex® ST505 PET by drawdownusing a #5 Meyer bar.

The sample was cured with a pulse length of 500 microseconds, andoverlap factor of 2 at 24 feet per minute in an air environment. Thecolor of the film changed from dark brown to a copper color indicatingsignificant conversion of the copper oxide to copper. The sheetresistance of the film was 2.2Ω/sq.

Example 7 Hexanediol Reducer

A copper oxide dispersion was produced by mixing 1.5 g NanoArc® copperoxide, 7.5 g deionized water, 0.08 g PVP K-30, 0.8 g ethylene glycol,0.03 g Tergitol® TMN-6, 0.02 g Dynol® 604, and 0.47 g 1,2-hexanediol ina 20 mL vial. 5 g of zirconium oxide milling media was added and thevial was agitated for 60 minutes.

The dispersion was applied to a sheet of Melinex® ST505 PET by drawdownusing a #5 Meyer bar.

The sample was cured with a pulse length of 600 microseconds, andoverlap factor of 2 at 24 feet per minute in an air environment.Although the film was not electrically conductive, the color of the filmchanged from dark brown to a copper color indicating significantconversion of the copper oxide to copper.

Example 8 Glutaric Acid Reducer

A copper oxide dispersion was produced by mixing 1.5 g<50 nm copper (II)oxide, 6.8 g deionized water, 0.08 g PVP K-30, 0.8 g ethylene glycol,0.03 g Tergitol® TMN-6, 0.02 g Dynol® 604, and 0.47 glutaric acid in a20 mL vial. 5 g of zirconium oxide milling media was added and the vialwas agitated for 60 minutes.

The dispersion was applied to a sheet of Melinex® ST505 PET by drawdownusing a #5 Meyer bar.

The sample was cured with a pulse length of 1,200 microseconds, andoverlap factor of 3 at 25 feet per minute in an air environment. Thecolor of the film changed from dark brown to a copper color indicatingsignificant conversion of the copper oxide to copper. The sheetresistance of the film was 2.7 Ω/sq.

Example 9 Polyacrylamide Reducer

A copper oxide dispersion was produced by mixing 1.75 g NanoArc® copperoxide, 5.3 g deionized water, 0.09 g PVP K-30, 0.6 g ethylene glycol,0.02 g Tergitol® TMN-6, 0.01 g Dynol® 604, and 1.25 g polyacrylamide ina 20 mL vial. 5 g of zirconium oxide milling media was added and thevial was agitated for 60 minutes.

The dispersion was applied to a sheet of Melinex® ST505 PET by drawdownusing a #5 Meyer bar.

The sample was cured with a pulse length of 800 microseconds, andoverlap factor of 2 at 24 feet per minute in an air environment.Although the film was not electrically conductive, the color of the filmchanged from dark brown to a copper color indicating significantconversion of the copper oxide to copper.

Example 10 Pentaerythritol Reducer

A copper oxide dispersion was produced by mixing 1.75 g NanoArc® copperoxide, 5.3 g deionized water, 0.09 g PVP K-30, 0.6 g ethylene glycol,0.02 g Tergitol® TMN-6, 0.01 g Dynol® 604, and 0.90 g pentaerythritol ina 20 mL vial. 5 g of zirconium oxide milling media was added and thevial was agitated for 60 minutes.

The dispersion was applied to a sheet of Melinex® ST505 PET by drawdownusing a #5 Meyer bar.

The sample was cured with a pulse length of 600 microseconds, andoverlap factor of 2 at 24 feet per minute in an air environment.Although the film was not electrically conductive, the color of the filmchanged from dark brown to a copper color indicating significantconversion of the copper oxide to copper.

Example 11 Succinic Acid Reducer

A copper oxide dispersion was produced by mixing 1.75 g NanoArc® copperoxide, 5.3 g deionized water, 0.09 g PVP K-30, 0.6 g ethylene glycol,0.02 g Tergitol® TMN-6, 0.01 g Dynol® 604, and 0.71 g succinic acid(sodium salt) in a 20 mL vial. 5 g of zirconium oxide milling media wasadded and the vial was agitated for 60 minutes.

The dispersion was applied to a sheet of Melinex® ST505 PET by drawdownusing a #5 Meyer bar.

The sample was cured with a pulse length of 700 microseconds, andoverlap factor of 4 at 24 feet per minute in an air environment.Although the film was not electrically conductive, the color of the filmchanged from dark brown to a copper color indicating significantconversion of the copper oxide to copper.

Example 12 Carbon Reducer

A copper oxide dispersion was produced by mixing 1.75 g NanoArc® copperoxide, 5.3 g deionized water, 0.09 g PVP K-30, 0.6 g ethylene glycol,0.02 g Tergitol® TMN-6, 0.01 g Dynol® 604, and 0.32 g carbon black in a20 mL vial. 5 g of zirconium oxide milling media was added and the vialwas agitated for 60 minutes.

The dispersion was applied to a sheet of Melinex® ST505 PET by drawdownusing a #5 Meyer bar.

The sample was cured with a pulse length of 500 microseconds, andoverlap factor of 2 at 24 feet per minute for four passes in an airenvironment. Although the film was not electrically conductive, thecolor of the film changed from dark brown to a copper color indicatingsignificant conversion of the copper oxide to copper.

Example 13 Uric Acid Reducer

A copper oxide dispersion was produced by mixing 1.75 g NanoArc® copperoxide, 5.3 g deionized water, 0.09 g PVP K-30, 0.6 g ethylene glycol,0.02 g Tergitol® TMN-6, 0.01 g Dynol® 604, and 0.89 g uric acid in a 20mL vial. 5 g of zirconium oxide milling media was added and the vial wasagitated for 60 minutes.

The dispersion was applied to a sheet of Melinex® ST505 PET by drawdownusing a #5 Meyer bar.

The sample was cured with a pulse length of 600 microseconds, andoverlap factor of 2 at 24 feet per minute for four passes in an airenvironment. Although the film was not electrically conductive, thecolor of the film changed from dark brown to a copper color indicatingsignificant conversion of the copper oxide to copper.

Example 14 Inkjet with Glycerol Reducer

A copper oxide dispersion was produced by first milling a mixture of52.5 g NanoArc® copper oxide, 2.6 g PVP K-30, and 294.9 g deionizedwater. The resulting average particle size was 115 nm. An inkjet ink wasproduced by mixing 8.4 g of the milled copper oxide dispersion, 1.0 gglycerol, 0.5 g ethylene glycol, 0.04 g Triton® X-100, and 0.03 gBYK®-020.

The inkjet ink was printed using a desktop inkjet printer onto Pictoricobrand PET.

The sample was cured with a pulse length of 300 microseconds, andoverlap factor of 2 at 24 feet per minute in an air environment. Thecolor of the film changed from dark brown to a copper color indicatingsignificant conversion of the copper oxide to copper. The sheetresistance of the film was 1Ω/sq.

Example 15 Copper Powder with Ascorbic Acid and Glycerol Reducer

A copper dispersion was produced by mixing 2.5 g of Mitsui copperpowder, 0.04 g of BYK®-020, 0.04 g of Tergitol® TMN-6, 0.25 g of PVPK-30, 0.89 g of glycerol, 0.45 g of ethylene glycol, 0.76 g of ascorbicacid in 7.57 g of deionized water.

The dispersion was applied to a sheet of Pictorico brand PET by drawdownusing a #10 Meyer bar.

The sample was cured with a pulse length of 1,000 microseconds, andoverlap factor of 4 at 24 feet per minute in an air environment. Thecolor of the film changed from dark brown to a copper color indicatingsignificant conversion of the copper oxide to copper. The sheetresistance of the film was 40 mΩ/sq. Assuming the film was fully dense,it was 1.3 microns thick and thus had a bulk conductivity of 5.2 microΩ-cm or 3.0 times the bulk resistivity of pure copper.

Example 16 Inkjet with Ascorbic Acid Reducer

A copper oxide dispersion was produced by first milling a mixture of52.5 g NanoArc® copper oxide, 2.6 g PVP K-30, and 294.9 g deionizedwater. The resulting average particle size was 115 nm. A first inkjetink was produced by mixing 8.4 g of the milled copper oxide dispersion,1.0 g glycerol, 0.5 g ethylene glycol, 0.04 g Triton® X-100, and 0.03 gBYK®-020. A second inkjet ink was produced by mixing 0.1 g of BYK®-020,0.2 g of Triton® X-100, 10.0 g of ascorbic acid, 3.0 g of ethyleneglycol, 4.5 g of glycerol in 42.5 g of deionized water.

Both inkjet inks were printed sequentially using an inkjet printer ontoPictorico brand PET.

The sample was cured with a pulse length of 1,000 microseconds, andoverlap factor of 1 at 24 feet per minute in an air environment. Thecolor of the film changed from dark brown to a copper color indicatingsignificant conversion of the copper oxide to copper. The film wasestimated to be 0.3 micron thick and had a sheet resistance of 140 mΩ/sqindicating a bulk conductivity of 4.1 micro Ω-cm or 2.4 times the bulkresistivity of pure copper.

All of the above-mentioned examples were prepared identically and placedin an oven containing an air environment at 150° C. for 30 minutes. Inall cases, there was no visual evidence of conversion or conductivity ofthe film. Higher oven temperatures were not possible since the highestworking temperature of PET is 150° C. When higher temperaturesubstrates, such as Kaptan or glass were used, no conversion was seeneven at temperatures up to 800° C.

Example 17 Copper Sulphate with Ascorbic Acid Reducer

A first solution was made with 20 wt % CuSO₄.5H₂O in deionized water. Asecond solution was produced by mixing 0.1 g of BYK®-020, 0.2 g ofTriton® X-100, 10.0 g of ascorbic acid, 3.0 g of ethylene glycol, 4.5 gof glycerol in 42.5 g of deionized water.

The first solution was deposited on ordinary photocopy paper by drawdownusing a #10 Meyer bar. This was followed by a deposition of the secondsolution by drawdown using a #5 bar.

The sample was cured with a pulse length of 1,000 microseconds, andoverlap factor of 4 at 24 feet per minute for three passes in an airenvironment. Although the film was not electrically conductive, thecolor of the film changed from dark brown to a copper color indicatingsignificant conversion of the copper oxide to copper. Under a lowmagnification microscope it was observed that the copper coated thefibers of the paper.

Example 18 Aluminum Reducer

A dispersion was made with 0.29 g of Valimet-H2 aluminum powder, 0.77 gof <5 micron copper (II) oxide from Sigma-Aldrich, 0.11 g of PVP K-30 in6.0 g of deionized water.

The dispersion was applied to a sheet of Pictorico brand PET by drawdownusing a #10 Meyer bar.

The sample was cured with a pulse length of 1,000 microseconds, andoverlap factor of 2 at 28 feet per minute in an air environment.Although the film was not electrically conductive, the film convertedfrom a dark brown to a copper color.

In contrast, identical films were prepared in all of the above exampleswere placed in an oven containing an air atmosphere at 150° C. for 30minutes. 150° C. was chosen since it is the highest working temperaturefor PET. No conversion was observed, and no films had any measurableelectrical resistance (greater than 400 MΩ/square).

While the invention has been particularly shown and described withreference to a preferred embodiment, it will be understood by thoseskilled in the art that various changes in form and detail may be madetherein without departing from the spirit and scope of the invention.

What is claimed is:
 1. A method for producing an electrically conductivethin film on a substrate, said method comprising: dispersing copperpowder, ascorbic acid and glycerol in a liquid; depositing saiddispersion on a non-conductive substrate as a thin film; exposing saidthin film along with said substrate to a pulsed electromagnetic emissionin an ambient atmosphere to chemically react said reducible metalcompound with metal oxides that may form and said reducing agent torender said thin film electrically conductive.
 2. A method for reducingthin films on low-temperature substrates, said method comprising:dispersing copper sulphate in a first liquid; dispersing ascorbic acidand glycerol in a second liquid; depositing said first and seconddispersions on a non-conductive substrate as a thin film; and exposingsaid thin film along with said substrate to a pulsed electromagneticemission in an ambient atmosphere in order to initiate a redox reactionbetween said reducible metal compound and said reducing agent on saidsubstrate.